Mpinge section – Exposures of the Upper African Surface, Chikonyora hill
Submitted by Andrew du Toit on Mon, 15/08/2016 - 11:04 | Last updated: Tue, 23/08/2016 - 13:30
Grid Ref (WGS84 Lat/Long in decimal degrees)
Turn-off north from the Mvurwi - Guruve tarred road near the western contact of the Great Dyke, pass through the mining areas and follow the track north along the Dyke to the base of Chikonyora Hill. From the grid reference above you can walk up to the beacon and mining workings.
Great Dyke Erosion Surfaces
At this stop (in the axis of the Great Dyke towards the northern end of the Mpinge section) can be seen the principal regolith stratigraphy of the Upper African Surface exposed around and above old chromite workings on the southern slopes of Chikonyora hill (1729m).
On the way, after the turn-off from the Mvurwi - Guruve tarred road, and to the right of the dirt road, look out for soil-mining areas and the mill and slimes dam of the old Mpinge eluvial chromite operation (1970s); also a good example of a butte (isolated hill with steep sides and a flat top similar to but narrower than a mesa: north American geomorphological term) of the Upper African Surface.
At this stop, a short traverse up the flanks of Chikonyora hill to the north displays the regolith stratigraphy of a broad Upper African mesa (extending 3km to the north) from the concave lower slopes, via a cliff-like feature, to the wooded ferruginous silicified zone of a well developed silica cap.
Note the following:
1. This part of the Mpinge section features a long, wooded ridge on the west side marking the P7 Pyroxenite at the base of the Dunite Succession.
2. The cliffs of the Upper African Surface are visible to the east and south east, and to the west.
3. Samples of serpentinite saprolite from outside the collapsed chromite workings are enriched in nickel (probably mainly in nickeloan serpentine and goethite). It may be possible to locate discrete, fracture-related, green, ‘garnierite-type’ hydrated Ni-Mg silicate minerals.
4. The ferruginous silicified zone is best seen on the high wooded ground above the workings.
NB. Also of interest is the fact that it was from Mpinge section that bulk samples of nickel laterite and eluvial chromite concentrates were used to produce ferronickel and stainless steel alloy in successful electric arc smelting test-work at the Institute of Mining Research, UZ, in the 1970s. (See Slatter, D.L., 1979. Production of ferrochrome nickel alloys and stainless steel by direct smelting of oxide ores in Zimbabwe-Rhodesia. Transactions of The Institution of Mining and Metallurgy (Section C: Mineral Processing and Extractive Metallurgy), 88, C209-214. Slatter, D.L., 1981. The potential for the direct production of ferrochromium nickel alloys and stainless steel ‘pig’ in Zimbabwe. In: INFACON 80: Proceedings of the Second International Ferro-alloys Congress, Lausanne, October 1980 (Lausanne: IPFED, Institut des Producteurs de Ferro-Alliages d’Europe Occidentale), 233-243.)
1) Zimbabwe Geological Survey Bulletin 90 - The Erosion Surfaces of Zimbabwe, L.A Lister 1987. 2) Landscape Evolution, Regolith Formation and Nickel Laterite Develoment in the Northern part of the Great Dyke, Zimbabwe, M.D. Prendergast. South African Journal of Geology, v. 116, i. 2, p. 219-240, December 2013